The present invention generally relates to an optical crossconnect apparatus for switching an optical transmission path, and also to an optical transmission system. More specifically, the present invention is directed to an optical crossconnect apparatus capable of recovering a failure of an optical transmission system under economical good connection, and also to an optical network.
Very recently, information infrastructures are prepared and maintained in order to widely progress a so-called xe2x80x9cmultimediaxe2x80x9d typically known as the Internet and CATV in society. To establish highly advanced information social structures, presently available information transmission amounts per one user are considerably increased. To this end, optical fiber networks capable of achieving wide ranges/low loss transmissions are introduced in transport backbones capable of performing long-hand/high-capacity transmissions. In a certain trunk line system constructed of optical fiber network, 10-Gbit data per second may be transmitted in unit of 1 optical fiber. As a result, failures, or troubles occurred in transmission paths, or lines would give serious adverse influences to society, and it is, therefore, very important to maintain the qualities of the network services even when failures happen to occur in transmission paths.
In order that reliability of networks is increased, transmission paths are effectively utilized, and also maintenance operation of transmission path is improved when failures happen to occur, optical crossconnect apparatuses have been positively developed. An optical crossconnect apparatus is installed between optical transmitters/receivers and optical fibers functioning as transmission paths within 1 node of an optical fiber network, and this optical crossconnect apparatus switches optical transmission paths to which optical input/output signals of the optical transmitter/receiver. With employment of such a function, for instance, in the case that a failure happens to occur in a certain working fiber, two sets of optical crossconnect apparatuses provided on both ends of this working fiber switch the connection destination of the optical transmitter/receiver to a protection fiber, so that the failure occurred in the transmission path can be restored.
On the other hand, in an actual optical network, a sufficient amount of protection fibers are not always installed among all of nodes. Accordingly, when a transmission path is recovered from a failure, while using the protection fiber installed between the nodes provided at both ends of the optical fiber where the failure happens to occur, and a third node, an optical signal must be rerouted to another route where no failure occurs so as to recover the failure-occurred transmission path. To reroute an optical signal, the transmission length would be extended, and the optical crossconnect apparatus itself of this third node would have loss. To avoid such an insertion loss, an optical signal repeating function is necessarily required for this optical crossconnect apparatus. This repeating function can be realized by that an optical repeater such as an optical amplifier and a regenerator is built in this optical crossconnect apparatus.
As the optical crossconnect apparatus having such an arrangement, for instance, one optical crossconnect apparatus is described in Japanese Electronic Telecommunication Institute Communication Society Conference held in 1996, publication B-1070, on page 555. Another optical crossconnect apparatus having no optical signal repeating function is described in Japanese Electronic Telecommunication Institute Communication Society Conference held in 1996, publication B-1083, on page 568.
Furthermore, the optical crossconnect technique is disclosed in Japanese Electronic Telecommunication Communication Institute, Autumn Conference held in 1993 publication SB-8-1, 4-371, on page 372.
An object of the present invention is to provide an optical crossconnect apparatus capable of effectively using protection fibers and optical repeaters, and further to provide an optical transmission system capable of recovering failure-occurred transmission paths in low cost.
Another object of the present invention is to provide such an optical crossconnect apparatus capable of monitoring optical signal penetrating conditions within an optical signal path of this optical crossconnect apparatus, and also capable of effectively identifying a place where a failure happens to occur when this failure occurs.
A further object of the present invention is to provide an optical crossconnect apparatus capable of executing a self-fail diagnosis of such an optical switch unit having occurrence probability of a failure among optical switch units for switching two sets of working transmission path and protection transmission path, and further capable of shortening failure restoration time.
A still further object of the present invention is to provide such an optical transmission system capable of confirming operation reliability/failure restoration related to a switched-destination, or a switched-back optical transmission path, and further to an optical switch units employed in the above-described optical crossconnect apparatus.
An optical crossconnect apparatus, according to a first aspect of the present invention, is featured by that an optical input unit is connected to an input of an optical signal repeater by an optical signal switching unit, and also an output of this optical signal repeater is connected to an optical output unit by an optical signal switching unit in such a manner that a protection fiber is connected to the optical signal repeater in a flexible manner. As a result, when the optical crossconnect apparatus equipped with the optical signal repeater mutually connects the protection fibers, since this optical crossconnect apparatus owns the optical signal switching unit capable of selecting such a protection fiber connected to the optical signal repeater, no longer the optical signal repeaters are prepared for the respective protection fibers. Thus, the optical crossconnect apparatus can be manufactured in low cost. Also, since the optical crossconnect apparatus employs the optical signal switching unit capable of selecting the optical signal repeater connected to the protection fiber, even when a failure happens to occur in the optical signal repeater, the optical transmission path can be immediately switched to the optical signal repeater operated under normal condition. As a result, the optical crossconnect apparatus having high reliability can be realized.
An optical crossconnect apparatus for switching transmission paths of an optical transmission signal by employing an optical switch unit, according to a second aspect of the present invention, is featured by comprising: an optical signal monitoring unit provided between an optical transmission signal input unit and the optical switch unit; either a signal source built therein or an external signal source; and a unit for sending out a monitoring optical signal supplied from, for example, a protection transmitter unit of an optical transmission terminal station apparatus.
An optical crossconnect apparatus for switching transmission paths of an optical transmission signal by employing an optical switch unit, according to a third aspect of the present invention, is featured by comprising: an optical signal monitoring unit provided between an optical transmission signal input unit and the optical switch unit; and an optical signal monitoring unit provided between the optical switch unit and an optical transmission signal output unit. This optical crossconnect apparatus can have such a function that a condition of an optical transmission signal of an input unit of this optical switch unit is compared with a condition of an optical transmission signal of an output unit of this optical switch unit by employing output signals derived from these two optical signal monitoring units, so that a failure of the optical switch unit is diagnosed.
Also, the optical crossconnect apparatus is further comprised of a first optical switch unit and a second optical switch unit, and also two sets of working optical switch unit and protection optical switch unit. The first optical switch unit selects the optical transmission signal, or the monitoring optical signal, which is entered into two sets of optical switch units. The second optical switch unit selects as to whether the output signal from each of the two optical switch units is directed to an optical transmission line, or an optical signal monitoring unit. The optical crossconnect apparatus can have such functions that this optical crossconnect apparatus confirms that the optical switch unit is operated under normal condition, and also identifies a place when a failure happens to occur, while using the monitoring optical signal and the output from the optical signal monitoring unit.
The optical crossconnect apparatus can further have such functions that this optical crossconnect apparatus confirms that the protection optical transmission path is set under normal state during the normal operation, and also confirms that the working optical transmission path is recovered from the failure during the failure occurrence condition, while the monitoring optical signal is sent to the protection optical transmission path during the normal operation, the monitoring optical signal is sent to the working optical transmission path during the failure occurrence condition.
With employment of the above-described arrangement, the optical crossconnect apparatus can monitor the penetration condition of the optical signal in the signal path of the optical crossconnect apparatus, and further can effectively identify the failure occurrence place when the failure happens to occur. Also, since the monitoring optical signal source is employed, such an optical switch unit that a failure may occur can be self-diagnosed within two sets of the working/protection optical transmission paths switching switch units. Thus, the failure restoration time may be reduced.
Furthermore, in accordance with the present invention, the conditions within the optical crossconnect apparatus, or the conditions of the optical transmission path can be monitored by employing the monitoring optical signal. The operation reliability and the failure restoration as to the switched destination optical transmission path, or the switched back optical transmission path, and further the optical switch units employed in the optical crossconnect apparatus can be confirmed.
An optical transmission system, according to a fourth aspect of the present invention, is featured by comprising a plurality of optical crossconnect apparatuses, and an optical transmission path for connecting the respective optical crossconnect apparatuses. The plural optical crossconnect apparatuses contain a plurality of optical transmitters/receivers, a first optical signal switching unit and a second signal switching unit, which are connected to the respective optical transmitters/receivers, and own ports through which optical signal can pass. The optical crossconnect apparatuses further contain an optical signal repeater, one terminal of which is connected to the port of the first optical signal switching unit, and the other terminal of which is connected to the port of the second optical signal switching unit. As a result, the optical transmitters/receivers communicate the optical transmission signal through the optical transmission paths except for an optical transmission path where a failure happens to occur, depending upon the occurrence of the failure. As a consequence, since the optical crossconnect apparatus according to the present invention is employed, a total number of optical signal repeaters employed in the overall optical transmission system can be reduced, and the optical signal repeaters can be quickly restored from the failure. Furthermore, since the protection optical fiber can be effectively utilized, the optical transmission system with high reliability can be manufactured in low cost.